The invention relates to a process for controlling an automatic transmission where an electronic transmission control, during a gear shift, determines the actual gradient from a transmission input rotational speed by comparing the actual with a standard value and determining the divergence. The clutches involved in the gear shift are then regulated so that the divergence is reduced between actual and set gradient of the transmission input rotational speed.
In automatic transmissions, the shift time determines the comfort of a gear shift. Shift time is understood as the space of time during which a transmission input rotational speed changes from a rotational speed level of a first reduction ratio to a rotational speed level of a second rotational speed ratio. Shift time that is too short causes a definite jolt. A shift time that is too long causes an excessively great heat input in the clutches involved in the gear shift. To this extent, the shift time represents a compromise between the two extremes mentioned above. A process for control/regulation of a gear shift is proposed, e.g. in EP-PS 0 339 664. In this process, shift time is adjusted by calculating an actual gradient from the transmission input rotational speed and comparing it to a set gradient.
In practice, however, it has been demonstrated that many drivers subjectively find bad constant shift time. Therefore, the problem which the invention solves is to more intimately combine the behavior of the automatic transmission with the driver""s behavior.
A first inventive solution consists of a first mode of driving in which electronic transmission control cyclically calculates driving activity from input variables of the vehicle and the driver, and changes the set gradient of the transmission input rotational speed according to the driving activity. In a second mode of driving, the electronic transmission control selects a special program from several, and changes the set gradient of the transmission input rotational speed according to the selected special program. As stated in claim 2, in the first mode of driving, the set gradient is changed in the sense that a high set gradient is adjusted during high driving activity.
The inventive solution and the development thereof offer the advantage that a driver""s behavior determines the shift sequences. In comfort-oriented driving mode, there results smooth, long gear shifts. From a sport mode of driving short gear shifts result. In automatic transmissions having a so-called xe2x80x9cintelligentxe2x80x9d shift program, a driving activity is calculated for selecting the shift points. Such processes have been disclosed, e.g. in DE-PS 39 22 051 and DE-OS 39 41 999. The inventive solution results in the added advantages that the already determined driving activity can be returned to and the inventive solution can be economically integrated via existing software.
In one development of the invention, it is proposed that in the second mode of operation, the set gradient of the transmission input rotational speed be changed in direction of lower values when one of the following special programs is active: winter program, slip regulation of the input gears, cruise control function, or city program. The effect of the development is that the gear shifts are very smoothly performed and, e.g. in the winter program, unsafe driving situations are prevented.
In a further development of the invention, it is proposed that in the second mode of operation the set gradient of the transmission input rotational speed be changed in a direction of higher values, i.e. to a short shift time, when one of the special programs such as mountain/trailer, or downhill is active. An advantage results when driving uphill with a trailer when due to the short shift time after the gear shift, a sufficiently high acceleration capacity is available.
In a second inventive solution of the problem, it is proposed that the electronic transmission control change the set gradient of the transmission input rotational speed, depending on a shift program activated by means of a program selector switch. The inventive solution can be preferably used in conventional automatic transmissions. In conventional automatic transmissions, the driver can select, via a switch, e.g. between economical xe2x80x9cExe2x80x9d, sporting xe2x80x9cSxe2x80x9d and winter xe2x80x9cWxe2x80x9d programs.